Web offset printing utilizes a continuous web of paper upon which printing or pictorial indicia may be printed. Typically, the web, or roll of unprinted paper or plastic material, is dispensed from a roll stand and supplied to offset print stations which function to apply ink to the web in a predetermined pattern. The printed web is later provided to further processing apparatus which may variously function to rewind the web into a finished roll or to cut the web into sheets for folding or stacking. However, if the ink is not thoroughly dry, "set-off" or transfer of the ink to adjacent or overlying web material will occur. Thus, drying or curing of the ink is of paramount importance to the printing process.
In order to facilitate drying of the print, several techniques have been devised. For example, prior systems have employed hot air blowers and more recently infrared heaters to heat the printed web to hasten the drying process. A more modern technique of hastening the drying process is with an ultraviolet (UV) curing system which functions to expose the printed web to large amounts of ultraviolet radiation. Generally, these prior techniques are limited in drying or curing speed by temperature considerations and thus represent the time-limiting factor in continuous web printing. Further, the prior techniques require large amounts of energy thus increasing the cost of such systems.
While the UV curing systems are an improvement over the hot air blowers and infrared systems, the UV curing systems require specialized inks and coatings which tend to be expensive. Additionally, the UV curing technique is color sensitive, some colors curing more rapidly than others and the overall result is a relatively slow curing process. Further, certain UV inks do not perform well on certain webs or substrates. Variations in UV lamp life can also present problems, since as lamps become weaker, quality variations begin to appear.
The above-mentioned techniques for hastening the drying process of the ink all involve the transfer of a large amount of heat to the ink and webbing resulting in a deterioration of the webbing. Additionally, none of these techniques are rapid enough to cure extremely heavy layers of inks and coatings which may be desired for certain application.
Recently, new techniques for curing coatings, such as pressure sensitive adhesive coatings, or resin precursor coatings, employing electron beam radiation, have been devised. For example, U.S. Pat. No. 4,177,314 to Steeves teaches the use of a radiation curable resin for coating a paper substrate to provide a smooth resin film thereon. After applying the resin coating to the paper substrate, the coated substrate is immediately cured by exposing it to an electron beam "curtain" transverse to the movement of the substrate web. The electron beam machinery provides two to three megarads which is sufficient to cure the resin film within a few milliseconds of exposure to the beam. After curing the resin coating, standard printing may be applied to the smooth resin coating, the coating providing a smooth surface which absorbs very little of the ink applied thereon, yet which provides an improved surface for the adhesion of the ink thereto.
Another use of the electron beam curing technique is described by Nablo et al in U.S. Pat. No. 4,246,297, which describes the use of the electron beam curing technique for providing urethane or vinyl coatings on fabrics, or the provision of phenolic insulating coatings on wires. In particular, the patent to Nablo describes the curing of a coating layer formed on a substrate of either fabric or "release" paper. After curing, the release paper is separated from the coating.